Abstract: 19 fetuses at the fertiligation age of 2—9 months,aborted non-pathologically and non-pharmacally,were studied.The haemopoiesis in different sites of bone marrow was observed in 17 cases, PAS staining of the nucleated red cell in 19 cases and ANAE staining of the marrow lymphocytes were studied in one at the fertilization age of 7 months and another at 8.Cardiac blood smears of 11 fetuses were also stained with ANAE.The results are as follows:（1）Fetal marrow haemopoiesis begins in the third month of fetal development,and the bone marrow becomes more cellular and extended as fetus develops.（2）The clavicle may seems to be the first site of haemopoiesis,while the sterum is the last.（3）The M/E ratio is reversal in whole fetal life,the erythroid series and its aberrant rate are higher during the earier and later periods.（4）Marrow lymphocytes reach their peak in the sixth month.（5）Osteoblasts predominate and remain the most numerous cells in the early period of marrow haemopiesis and decrease in number as the fetus develops.（6） PAS score of nucleated red cells has little difference during postnatal period,but there are differences at various fetal ages.（7）ANAE-positive lymphocytes in cardiac blood smears during prenatal period are much less than those during postnatal period,but much more than those in marrow of the same fertiligation age.